The present invention relates to an improved control mechanism for an offset printing machine which causes a first sheet printed to have the same density as subsequent sheets.
In a well known offset printing machine, ink is applied to a cylindrical plate carrying a printing image and a transfer roller picks up the ink image from the plate and transfers the same to sheets, thereby effecting printing. A problem exists in the initial stage of operation of this type of printing machine in that it takes a certain amount of time to build up enough ink on the plate and transfer roller that the printed image on the sheets is of sufficient density. There is a certain amount of time after initiating the application of ink in which the ink buildup in optimum for printing. If the first sheet is fed to the transfer roller at exactly this time, the first sheet and all subsequent sheets will be printed with optimum density.
However, if the first sheet is fed at the same time the inking operation is started, the printing density of the first sheet or two will be too low, thereby wasting at least one sheet and requiring a further process step of removing the first sheet from the rest for disposal. Offset printing machines to date do not comprise an automatic means for feeding the first sheet at the correct time after inking begins.